The present invention relates to the production of an optical module used for optical communication system such as a data link and an optical LAN using light as data transmitting medium, more particularly to an optical sub-module including at least one optical operation element such as a light emitting element or a light receiving element which is optically connected to an optical fiber, an optical module comprising the sub-module and a receptacle.
A single-core optical sub-module including a single optical operation element optically connected to an optical fiber, is made into one of two types. That is, one is a transmission sub-module using a light emitting element such as a semiconductor laser as the optical operation element, and the other is a receiving sub-module using a light receiving element such as a pinphoto diode as the optical operation element.
FIG. 1 shows a conventional single-core optical sub-module. In the conventional single-core optical sub-module, after an optical axis of an optical operation element 2 such as a light emitting element or a light receiving element is aligned, the optical operation element is fixed to an optical connector 1 fitted to a ferrule (not shown) fixed to an end portion of an optical fiber (not shown) by an adhesive and the like. The optical connector 1 fixing the optical operation element 2 is fixed to a ceramic package 3 by an adhesive and the like. In addition to the optical connector 1, a substrate 6 supporting an electronic circuit portion composed of electronic circuit parts such as a bare chip IC 5 is fixed to the ceramic package 3. The bare chip IC 5 and the like on the substrate 6 as well as wires for connecting the bare chip IC to a wiring pattern of the substrate 6 are sealed by a lid 7. Also, the ceramic package 3 is provided with lead pins 8 including inner leads 8a provided inside the package and outer leads 8b provided outside the package. The inner leads 8a and the electronic circuit portion on the substrate 6, as well as the electronic circuit portion and a terminal of the optical operation element 2 are electrically connected by wire bonding and the like. Then, a cover 10 is fixed to the ceramic package 3 so that the single-core optical sub-module is constructed.
As shown in FIGS. 2 and 3, a plurality of thus constructed single-core optical sub-modules 11 are attached to a receptacle 12 so that a conventional multi-core optical module is constructed.
In the thus constructed multi-core optical module, optical fibers are concurrently inserted in the respective optical connectors 1 so that a plurality of data links are formed at the same time.
The single-core optical sub-module 11 is constructed by many elements, and each element is assembled one by one. Thus, assembling steps are complicated, and many steps are required for the assembling. Further, since expensive materials such as ceramic are used, it is difficult to lower the cost and to mass-produce the single-core optical sub-module.
On the other hand, the conventional multi-core optical module is constructed by combining a plurality of single-core optical sub-modules 11. Accordingly, it is also difficult to lower the cost and to mass-produce the multi-core optical module composed of the plurality of single-core optical sub-modules. Further, at the practical use, the optical connectors are attached to and off a multi-core plug having a plurality of ferrules in the receptacle 12. Thus, when the single-core optical modules 11 are attached to the receptacle 12, high accuracy of positioning is required. That is, if the positioning accuracy is insufficient, smooth attachment and detachment of the optical connectors become impossible. In the worst case, partial abrasion or damage of the ferrules of the plug or the optical connectors 1 is caused. The positioning accuracy must be high as the number of optical connectors included in the multi-core optical module increases. For the multi-core optical module with more than three cores, very high positioning accuracy is required. Accordingly, assembling portions of the single-core optical sub-module 11 and the receptacle must be formed at high accuracy, and at the assembling, as shown in FIGS. 2 and 3, an alignment tool 15 including the same number of ferrules 13 as the optical connectors of the multi-core optical module must be used to carry out precise positioning.
Further, as shown in FIG. 4, when the multi-core optical module precisely positioned as described above is mounted on a printed circuit board 16 by screwing, soldering or the like, relative positional relation between the single-core optical sub-modules 11 or between the sub-modules 11 and the receptacle 12 may be distorted. In order to solve the problem, the alignment tool 15 must be attached to the multi-core optical module until the multi-core optical module is completely mounted. Therefore, operational efficiency of the mounting is inferior.